Log periodic radial arm-coupled loop antenna

ABSTRACT

A radial arm-coupled loop log-periodic antenna comprising a tapered mounting member with circular elements positioned thereon, one side of the elements having radials thereon for providing a sum mode, the other side of the elements having loops thereon for providing a difference mode pattern.

United States Patent [191 Corzine July 10, 1973 [54] LOG PERIODIC RADIALARM-COUPLED 3,ll0,030 ll/l963 Cole, .lr. 343/7925 LOQP ANTENNA [75]Inventor: g m" Comm Chma Lake Primary Examiner-Banjamin A. Borchelt aAssistant Examiner-Richard E. Berger [73] Assignee: The United States ofAmerica as Attorney-R. S. Sciascia and Roy Miller represented by theSecretary 0! the Navy, Washington, DC.

22 F1 d: 9 l 71 l 1 June 9 57 ABSTRACT [21] Appl. No.: 151,480 A radialarm-coupled loop log-periodic antenna com- [52] U.S. Cl 343/792.5,343/742, 343/908 prising a tapered mounting member with circular ele-[51] Int. Cl. ll0lq 1 1/10 ments positioned thereon, one side of theelements hav- [58] Field of Search 343/7925 ng radia s t ere forproviding a sum mode, the other side of the elements having loopsthereon for providing [56] 4 I References Cited a difference modepattern.

UNITED STATES PATENTS 2 Claims,-7 Drawing Figures PAIENIEU MI 0 m 3 Q745 5 84 sum 1 or 4 I NTENNA IN FoRwARD POSITION- AT HIGH FREQUENCIES ATHIGH FREQUENCIES ENERGY REFLECTS',

AT Low FREQUENCIES ENERGY PAssEs THROUGH AND NO' I PROBLEM ExIsTs I (LowFREQUENCIES ARE DEFINED BY w THAT SPECTRUM WHERE RADDME. I, wALL ISELEC-r g TRICALLY THIN) f r 1/] ANTE NA IN REAR f POSITION- I 1/ HIGHFREQUENCY v REFLECTIONS CAusE INTERFERENCE INVENTOR.

ROBERT G. CORZINE BY: ROY MILLER v ATTORNEY.

PAIENIEDJUHOW 3.745.584 sum 2 or 4 FIG. 2.

PAIENIEU JUL 1 0 I975 SHEET 3 0F 4 LOG PERIODIC RADIAL ARM-COUPLED LOOANTENNA CROSS REFERENCE TO RELATED APPLICATION Co-pending applicationSer. No. 106,883, filed Jan. 1971 titled Broad Band, PolarizationDiversity Monopulse Antenna by Robert G. Corzine, Bruce E. Bolstand andJohn S. Johangten.

BACKGROUND OF THE INVENTION ameter of the antenna, it is required thatthe planar spi-- ral be placed in a rearward position in the radome,making it particularly susceptible to radome internal reflections. Forreceiving signals of all polarizations, it is required that the spiralantenna be simultaneously excited from the center and the outerperiphery. To do this over multi-octave bandwidths requires many spiralelements and therefore complex, expensive, feed networks. The fact thatthe relative phase of the sum and difference modes does not remainconstant with changing frequency introduces additionally feed networkcomplexity and loss of gain for compensating the relative phase.

The conical spiral eliminates the backing cavity associated with theplanar spiral and therefore has better gain. However, the compensationof the relative phase of the sum and difference modes is much worse thanfor the planar spirals. As with the planar spiral, reception of allpolarizations requires simultaneous center and outer periphery feedingand the attendant feed network complexity. Additionally, the phasecenter of the sum mode is not coincident with the phase center of thedifference mode. This causes the relative phase of the sum anddifference modes to vary as a function of the angle between the antennaboresight and the target. Complexity is introduced in compensating forthis phenomena. The conical spiral functions fairly well within a radomein that high frequencies radiate near the tip of the conical spirals andlow frequencies toward the base of the cone. However, since the phasecenter of the difference mode is not as close to the tip of the cone asthe sum mode, it is slightly more subject to radome internal reflectionthan the sum mode.

Interferometer arrays of planar spirals are not frequency independentand receive circular polarization of one sense only without complexity.Log periodic dipole interferometers are'linearly polarized. Conicalspiral interferometers, when arrayed in a frequency independent manner,suffer aperture blockage and poor direction finding accuracy. Conicalspirals also receive circular polarization of one sense only withoutcomplexity. Phase sensing requires a minimum of three antenna elementsfor a monopulse direction finding in two planes.

Amplitude sensing systems provide relatively poor direction findingaccuracy. Measurement accuracy also requires component matchingrequirements.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a radome withantennas and reflections therein;

FIG. 2 illustrates the antenna construction;

FIG. 3 is top view of the element pattern;

FIG. 4 is the bottom view of the element pattern;

FIG. 5 is an illustration of the first element;

FIG. 6 is a fragmentary view of the wrapping of the wire around themetal post element; and

FIG. 7 is a section through FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates thereflection patterns that exist withina radome at high and lowfrequencies. The legends on the figure are self explanatory andillustrate problems which the present invention is intended to overcome.

FIG. 2 is a side elevation of the antenna structure illustrating a metalpost made of aluminum 10 or equivalent material having the antennaelements 11 positioned thereon. The antenna elements 11 are made fromconventional circuit board material and popped into a circumfrentialslot (not'shown) on the tapered shaft 10. In the present embodiment thepost 10 has a five degree taper, as does the overall array of elements11.

Six semirigid 50-ohm coaxial cables l2 run up the center of the metalshaft 10 to the tip of the array.

The individual elements 11 are spaced logarithmi-' cally along the metalshaft 10 in the relationship 1' (l,/l )(l /l )(l /l The individualelement patterns are shown in FIGS. 3 and 4. FIG. 3 illustrates the sixarm radial pattern which radiates the sum mode. The six arms areillustrated at 31 36, and are copper plated elements (using conventionalprinted circuit techniques) on the circuit board material. There is a 5taper to the individual radials and in the present exam.- ple thedistance from the center to the tip of the individual radials is (0.28)\where A wavelength. Optimumly, the radials should be one-fourthwavelength. A radius of 028A represents an optimum compromise. Holes 37are provided on the end of each arm of the radial for the wireconductors 12 shown in FIG. 2 Solder connections are made only on thesum radiating radials at holes 37 as shown in FIG. 6.

The bottom of the element pattern is shown in FIG. 4 and overlies thetop pattern of FIG. 3. The pattern of FIG. 4 is actually a loop whereinthe radius of the loop is 0.28% and the widthof the circumfrential loopis 0.04). Optimumly, the loop circumference should be two wavelengths.The loop circumference of l.76)\ represents an optimum compromise. Nophysical connection of the loop structure is made to the coaxial cables12.

FIG. 5 illustrates the first element used at the tip of the array in theconfiguration. The center conductor of each of the six coaxes 12 issoldered to the sum pattern radials at 51. Connections 52 to each of thesum radials are the starts of the external conductor 61 that is wrappedaround the center 10 post and illustrated in FIG. 6.

FIG. 6 is a fragmentary showing of the center post 10 with insulatingtape 11 thereon. External conductors 61 are illustrated wrapped in ahelix around the outer periphery of the center post 10 and soldered topoint 52 on each of the radials as illustrated in FIG. 3. As statedpreviously, no connection is made to the difference mode loopsillustrated in FIG. 4. The loops are capacitively coupled to the radialsof FIG. 3 on the reverse side of the individual elements.

FIG. 7 is a section through the antenna structure to show the arrangmentof coax cables and external conductors.

The advantages of the invention are: (l) broad-band formation of sum anddifference monopulse patterns (sum patterns from VHF to K band anddifference patterns from L band to K band for missile sized structures);(2) compatible with zero order mode, body cancelled current array forcontinuous UHF through K band coverage in missile configurations; (3)eliminates most internal reflections within radome in that the phasecenter is forward at high frequencies and moves aft as frequency isdecreased; (4) eliminates plane rotation compensation with frequencyrequirement; (5) phase centers for both sum, first order mode, anddifference (second order mode) are coincident across fre quency bandand; (6) polarization diversity is possible.

What is claimed is:

1. An antenna comprising;

a support structure having ends;

circular radiating elements having opposite sides and spaced apartlongitudinally on said support structure;

radiating members on at least one side of said radiating elements;

said radiating members comprising spoke-like means which radiate fromthe center of each of said elements; I

said radiating members being joined at the circumference of said elementby a continuous conductive member;

said radiating elements being so dimensioned that the phase center ofthe radiating structure is at one end of said support structure at highfrequencies and moves toward the other end of said structure asfrequency is decreased.

2. An antenna as set' forth in claim 1 including;

other radiating members on the other side of said radiating elements;

said other radiating members comprising spoke-like means which radiatefrom the center of the elements.

1. An antenna comprising; a support structure having ends; circularradiating elements having opposite sides and spaced apart longitudinallyon said support structure; radiating members on at least one side ofsaid radiating elements; said radiating members comprising spoke-likemeans which radiate from the center of each of said elements; saidradiating members being joined at the circumference of said element by acontinuous conductive member; said radiating elements being sodimensioned that the phase center of the radiating structure is at oneend of said support structure at high frequencies and moves toward theother end of said structure as frequency is decreased.
 2. An antenna asset forth in claim 1 including; other radiating members on the otherside of said radiating elements; said other radiating members comprisingspoke-like means which radiate from the center of the elements.